The document discusses the hydrogen spectral series, which consists of a sequence of spectral emissions arranged by wavelength. The series occur in the ultraviolet, visible, and infrared regions. Experimentally, hydrogen gas in a discharge tube is excited by a stream of electrons from a cathode. This causes electrons in hydrogen atoms to absorb energy and jump to higher energy orbits. When the electrons fall back down, they emit photons of specific wavelengths, producing the spectral lines. There are six hydrogen spectral series named after their discoverers - Lyman, Balmer, Paschen, Brackett, Pfund, and Humphreys. The Rydberg formula can be used to calculate the wavelengths of lines in the series based on the energy levels involved.
2. Hydrogen spectral series
The hydrogen spectral series consists of a sequence of spectral emissions
arranged based on their wavelengths in the electromagnetic region of the
hydrogen atomic spectrum.
These are the series of distinct and discrete spectral lines in the ultraviolet,
visible, and infrared regions of the electromagnetic spectrum.
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3. Hydrogen spectral series
• Experimentally, the discharge tube consists of
hydrogen gas at low pressure conditions.
• The discharge tube is an evacuated glass tube
that has metal electrodes at its ends that act as
cathode and anode.
• The stream of fast moving electrons that
produced from cathode travels towards anode
in the discharge tube.
• These accelerated electrons of the cathode rays
give internal energy to the hydrogen electrons
during their collision. Jayam chemistry learners
4. Hydrogen spectral series
• After gaining energy from the source, the
electrons of the hydrogen atoms get excited
from the ground state to one of the higher
energy orbits.
• As everyone knows, the excited state of an
atom is unstable. The excited electrons jump
back to its initial lower energy position
abruptly with the emission of light radiations
of definite wavelengths. It gives a sequence of
spectral lines in the hydrogen emission
spectrum. Jayam chemistry learners
Absorption of energy
Emission of energy
5. Hydrogen spectral series formula
The Rydberg formula helps to calculate the wavelengths of all spectral lines that occur in
the hydrogen spectrum with the help of an empirical fitting parameter known as the
Rydberg constant.
Where,
λ = wavelength of the emitted electromagnetic radiation
n1 = lower energy level of the electron transition
n2 = higher energy level of the electron transition
R= Rydberg constant with value equal to 109678 cm-1
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6. The six series of the hydrogen spectrum
• The six sequences of the hydrogen emission
spectrum correspond to the discontinuous
spectral line emissions due to quantized
electron energy levels of the hydrogen atom
explained by Niels Bohr.
• The six series of the hydrogen spectrum are;
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1. Lyman series 4. Brackett series
2. Balmer series 5. Pfund series
3. Paschen series 6. Humphreys series
7. Lyman series
• This series of spectral lines were observed
during electron transition from higher
stationary orbits to the first orbit of the
hydrogen atom.
• It is named after the discoverer Theodore
Lyman.
• And it occurs in the ultraviolet region of the
electromagnetic spectrum.
• The maximum wavelength for the Lyman
series is 121 nm and the minimum wavelength
is 91 nm. Jayam chemistry learners
8. Balmer series
• This series of spectral lines were observed
during electron transition from higher
stationary orbits to the second orbit of the
hydrogen atom.
• It is named after the discoverer Jakob Balmer.
• And it occurs in the visible region of the
electromagnetic spectrum.
• The maximum wavelength for the Balmer
series is 656 nm and the minimum wavelength
is 365 nm.
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Balmer series
9. Paschen series
• This series of spectral lines were observed
during electron transition from higher
stationary orbits to the third orbit of the
hydrogen atom.
• It is named after the discoverer Friedrich
Paschen.
• And it occurs in the infrared region of the
electromagnetic spectrum.
• The maximum wavelength for the Paschen
series is 1875 nm and the minimum
wavelength is 821 nm. Jayam chemistry learners
10. Brackett series
• This series of spectral lines were observed
during electron transition from higher
stationary orbits to the fourth orbit of the
hydrogen atom.
• It is named after the discoverer Sumner
Brackett.
• And it occurs in the infrared region of the
electromagnetic spectrum.
• The maximum wavelength for the Brackett
series is 4051 nm and the minimum
wavelength is 1458 nm. Jayam chemistry learners
11. Pfund series
• This series of spectral lines were observed
during electron transition from higher
stationary orbits to the fifth orbit of the
hydrogen atom.
• It is named after the discoverer Herman Pfund.
• And it occurs in the infrared region of the
electromagnetic spectrum.
• The maximum wavelength for the Pfund series
is 7460 nm and the minimum wavelength is
2280 nm.
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12. Humphreys series
• This series of spectral lines were observed
during electron transition from higher
stationary orbits to the sixth orbit of the
hydrogen atom.
• It is named after the discoverer Curtis J.
Humphreys.
• And it occurs in the infrared region of the
electromagnetic spectrum.
• The maximum wavelength for the Humphreys
series is 12.37 μm and the minimum
wavelength is 3.2 μm. Jayam chemistry learners
13. Why does the line spectrum of hydrogen lines become closer as the
frequency increases?
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Lyman series, the broad series of the hydrogen spectrum, gives thick spectral emissions
towards its end. Likewise, the Balmer and Paschen series are more compact when
compared with the Lyman series. We observe a thick spectral line region at the series limit
of every series. It is the position where the next series starts.
14. Why does the line spectrum of hydrogen lines become closer as the
frequency increases?
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According to the quantum theory of radiation, the energy difference between the
stationary levels varies directly with the frequency of the emitted light radiation. It
implies the frequency of the emitted photon is higher for electron transitions involving
higher transition states.
Moreover, the stationary orbits are not equally spaced. They are more close together at
higher energy levels. So, the electron transitions involving these closely spaced orbits
give spectral lines packed together.
As a final note, the dense spectral emissions towards the right end of the hydrogen
spectrum imply higher photon frequencies.
15. The end
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